Replaceable body parts sounds like something out of a science-fiction (or horror) movie. But for those who are missing limbs, in need of an organ transplant, or have vision or hearing impairments, it could mean a new lease on life thanks to the biomedical engineers who are up to the challenge.

One could envision a future where humans opt to have functioning body parts replaced with ones that can lend them superhuman abilities. But visions of cyborgs are quickly forgotten when a person who has lost their vision has it restored with a microchip-powered retinal implant or a professional dancer who lost her leg in a national tragedy is able to perform onstage again.

Testing the limits of just how much of the human body can be replicated and replaced, Swiss psychologist Bertolt Meyer worked with robotics engineers to create a robot modeled after himself. Meyer has a prosthetic arm—the i-limb ultra revolution— which was documented in the BBC documentary How to Build a Bionic Man. So he was well-positioned to assemble robot Rex from an array of prosthetics, even giving him a circulatory system. When faced with a robot with his own visage and a frustratingly clunky body, Meyer is initially distressed, but his concerns are quickly dismissed when Rex navigates the world well and draws admirers along the way.

While Rex is not fully replacing us anytime soon, he serves as a model for what's possible when technological ingenuity meets biology. Check out our slideshow for more examples.

1Skin

Artificial skin can feel real to a person touching it but might not provide much feeling to the transplant recipient. Using gold monolayer-capped nanoparticles, researchers at Technion-Israel Institute of Technology created e-skin that is 10 times more sensitive to touch than alternatives. The e-skin is flexible and able to detect pressure, temperature, and humidity.

2Skull

A woman in the Netherlands who suffers from a bone disorder had a thickening skull that threatened her life. Doctors at the University Medical Center Utrecht turned to 3D printing to create a new skull for her. With the pressure off her brain, difficulties that she had with vision and motor control disappeared.

A young girl in China was similarly saved by a titanium 3D-printed skull after suffering a serious case of hydrocephalus. Her head had grown four times its normal size. Physicians removed some of her skull, drained the fluid, and replaced the bone with the printed implant.

3Brain

Restoring lost brain function is often left up to the brain itself. But an artificial cerebellum-on-a-chip has been shown to restore lost brain function in rats. At Israel's Tel Aviv University, researchers disconnected a rat's cerebellum, which prevented it from blinking in reaction to a stimulus. After implanting the chip, they were able to teach the rat to blink in response. The researchers believe their findings can go beyond restoring functionality and enhance the brain's abilities.

Going beyond the rat model, a research team at the University of Pittsburgh Medical Center was able to outsource arm function from a man who has been a quadriplegic for 10 years to a robotic arm. By implanting two arrays of electrodes into the man's brain and then attaching a receiver to his skull, he is able to feel sensation via the arm and control it enough so that he can hold a glass and perform other tasks.

DARPA, meanwhile, is looking into brain implants that could result in enhancements to the mental capabilities of humans. The organization is committing $62 million to develop an implant that would transfer data between the brain and devices. The agency backhandedly acknowledges that its goal might not be feasible by noting that success would take "integrated breakthroughs across numerous disciplines including neuroscience, synthetic biology, low-power electronics, photonics, medical device packaging and manufacturing, systems engineering, and clinical testing."

4Eyes

Even when vision is 20/20, it's not straightforward. Seeing an image is a multi-step process, not a direct one, and it is carried out across a delicate neural web. At Stanford University, researchers are working on a photovoltaic retinal prosthesis to restore sight to those with blindness resulting from certain retinal conditions, such as retinitis pigmentosa and macular degeneration. The implant stimulates retinal neurons, completing the part of the visual process that is negatively affected by degenerative retinal diseases. Unlike previous implants that relied on extraocular power supplies, the Stanford team's implant gets its power by converting light into electrical current via a pair of glasses. The system is in clinical trials at the Quinze-Vingts National Eye Hospital in Paris.

5Ear

It's said that when you lose one of your senses, the others sharpen. Not wanting to leave that up to circumstantial evidence, Rich Lee, who was losing his vision, had headphones implanted in his ears by a body-modification artist. The headphones use magnets that work as speakers and a coil to transmit sound and greatly amplify what Lee hears so that he can navigate the world using echolocation.

6Jaw

A laser-sintered, 3D-printed jaw was successfully implanted from a woman who lost her own through a bone infection. The jaw was composed of thousands of layers and given a bioceramic coating. The solution was the work of doctors at Hasselt University in the Netherlands.

7Artificial Heart

The wait for a heart donor can be one that patients do not survive. To give them more time, researchers developed SynCardia, an artificial heart. SynCardia replaces valves and ventricles and works with an external power supply, letting patients leave the hospital and continue their lives. A word of caution though: there have been some issues recently, including a death that may have occurred as the result of a compressor failing.

8Arm

The Segway didn't go anywhere. But its inventor, Dean Kamen, has moved on to making a mind-controlled arm prosthesis. The Deka Arm is the size and weight of an average arm and allows small motor control great enough that the wearer can pick up a grape. The arm was developed as part of a DARPA project and has now received FDA approval.

9Leg

Hugh Herr has more motivation than most to build bionic legs—he wears them. After losing his legs to frostbite while rock climbing, he began to modify his prosthetics. Now he's the director of the Biomechatronics Group at the MIT Media Lab, and has led a team that's made leg prosthetics that move in a way that is more biological than mechanical. The robotic ankle-foot prosthesis the team designed is the first to enable a natural gait.

10Kidney

Researchers at Huazhong University of Science and Technology in China have made miniature, functioning kidneys through 3D printing. They are composed of 90 percent living cells and function almost exactly like real kidneys. With a few adjustments and advancements, it's possible that they will one day be ready for implanting into people.